Pressure relief rupture disk

Liquid effluent is collected in the drums, while gaseous overpressure is vented through a silica gel/ASZM-TEDA carbon filter. The waste handling system includes secondary spill containment for the drums, scales to measure liquid content, and pressure relief rupture disks. 

Type CG-1 (pressure relief rupture disk). A rupture disk (synonymous with the name burst disk within the industry) is a nonreclosing, pressure operated device that affords protection against development of excessive pressure in cylinders. This device is designed to rupture when the cylinder pressure is too high, thereby venting the entire contents of the cylinder. The rupturing of the rupture disk element results in a nonreclosing orifice. 

Caution The pressure relief rupture disk device is a primary safety component and the following guidelines should be followed ... 

Ap = differential pressure across liquid relief rupture disk, usually equals p, psig AP(dusts) = pressure differential, bar or psi... 

Used to indicate the inlet pressure and temperature of a pressure relief device at a specific overpressure. The relieving pressure is equal to the valve set pressure (or rupture disk burst pressure) plus the overpressure. The temperature of the flowing fluid at relieving conditions may be higher or lower than the operating temperature. 

This is a nonclosing differential pressure relief device designed to fxmction by bursting the pressure-containing rupture disk. A rupture disk device includes a rupture disk and a rupture disk holder. 

It is required to provide a suitable pressure relief device. If the transient analysis indicates an instantaneous increase in pressure, up to the PSV relief pressure, a rupture disk is needed to protect the system (because the PSV response time is much slower). However, the disadvantages of a rupture disk should also be considered before finalizing the type of protection required. 

Pressure-relief-device requirements are defined in Subsec. A. Set point and maximum pressure during relief are defined according to the service, the cause of overpressure, and the number of relief devices. Safety, safety relief, relief valves, rupture disk, breaking pin, and rules on tolerances for the reheving point are given. 

Pressure Relief Devices The most common method of overpressure protection is through the use of safety rehef valves and/or rupture disks which discharge into a containment vessel, a disposal system, or directly to the atmosphere (Fig. 26-13). Table 26-8 summarizes some of the device characteristics and the advantages. 

Rupture Disks A rupture disk is a device designed to function by the bursting of a pressure-retaining disk (Fig. 26-15). This assembly consists of a thin, circular membrane usually made of metal, plastic, or graphite that is firmly clamped in a disk holder. When the process reaches the bursting pressure of the disk, the disk ruptures and releases the pressure. Rupture disks can be installed alone or in combination with other types of devices. Once blown, rupture disks do not reseat thus, the entire contents of the upstream process equipment will be vented. Rupture disks are commonly used in series (upstream) with a relief valve to prevent corrosive fluids from contacting the metal parts of the valve. In addition, this combination is a reclosing system. 

FIG. 26 13 Typical pressure relief system configurations (a) rupture disk system (h) pressure relief valve system. 

Rupture disk device A non-reclosing pressure relief device actuated by inlet static pressure and designed to function by the bursting of a pressure containing disk. 

Rupture discs are also used below relief valves to protect them from corrosion due to ves.sel fluids. The rupture disc bursts first and the relief valve immediately opens. The relief valve reseals, limiting flow when the pressure declines. When this configuration is used, it is necessary to monitor the pressure in the space between the rupture disk and the relief valve, either with a pressure indicator or a high pressure switch. Othei-wise, if a pinhole leak develops in the rupture disk, the pressure would equalize on both sides, and the rupture disk would not rupture at its set pressure because it works on differential pressure. 

Vessel is final scrubber in a flare, relief, or vent system, i.s designed to withstand maximum built-up back-pressure, and is equipped with a rupture disk or safety head (PSE) to bypass any internal or external obstructions, such as mist extractors back-pressure valves, or flame arrestors. 

An important case of gas discliarge is tlie flow from pressure relief valves and rupture disks. Wlien relief is required due to fire exposure in a nonreacting... 

Rupture disks may be used to satisfy the requirements of the code for conditions such as corrosion and polymer formations, which might make the safety/relief valve inoperative, or where small leakage by a safety valve cannot be tolerated. They are particularly helpful for internal explosion pressure release. 

Figure 7-11. Safety valve and rupture disk installation using pressure rupturing disk on inlet to safety relief valve, and low pressure disk on valve discharge to protect against back flow/con-osion of fluid on valve discharge side, possibly discharge manifold. By permission, Fike Metal Products Div., Fike Corporation, Inc.

The capacity of the combination of the rupture disk device and the spring loaded safety or safety relief v alve may be established in accordance with the appropriate paragraphs of UG-132, Certification of Capacity of Safety Relief Valves in Combination with Non-reclosing Pressure Relief Devices. 

The space between a rupture disk device and a safety or safety relief v alv e shall be provided with a pressure gauge, a try cock, free vent, or suitable telltale indicator. This arrangement permits detection of disk rupture or leakage. ... 

Users are warned that a rupture disk wdll not burst at its design pressure if back pressure builds up in the space between the disk and the safety or safety relief valve which will occur should leakage develop in the rupture disk due to corrosion or otlier cause. 

Users are warned that an ordinary spring loaded safety relief valve will not open at its set pressure if back pressure builds up in the space between the valve and rupture disk. A specially designed valve is required, such as a diaphragm valve or a valve equipped with a bellows above the disk. 

WThen the pressure rise in a system is gradual and not explosive in nature, a safety or safety relief valve is the proper detdce, but when it is critical to completely depressure a system or the rate of pressure increase might be expected to be rapid, then a rupture disk is the proper device. Properly designed a pilot operated valve may be selected after checking its performance with the manufacturer. 

Often a system (a group of vessels not capable of being isolated from each other by block valves, or containing restriction to flow and release of pressure) may need a relief valve set reasonably close, sat +15% to 20% when system is below 1000 psig above, typically use 7% to 15% above as set criteria related to normal operating pressure to catch any pressure upswing. Then this may have a backup valve set higher (but within code) to handle further pressure increase. Or, the second device may be a rupture disk. It is not unusual to have two relief de ices on the same equipment set at different pressures. 

Never place a block valve on the inlet side of a pressure relief device of any kind, unless it conforms to the code practice for rupture disks or locking devices. See [1] Par. UG-135(e) and Appendix M, ASME code. 

Typical rupture disk assembly installed in combination with a pressure relief valve... 

Rupture disks are often placed below a safety valve to prevent corrosive, tarring or other material from entering the valve nozzle. Only disks which do not disintegrate when they burst (Figures 7-10, 7-11, 7-12, 7-18) can be used below a safety valve, as foreign pieces which enter the valve might render it useless. This is acceptable to certain code applications [1]. These disks are also used to pro dde secondary relief when in parallel tvith safety valves set at lower pressures. They can also be installed on the discharge of a safety valve to prevent loss of hazardous vapors, but caution should be used in anv serious situation. 

V Tiere the pressure relief valve is used in series with a rupture disk, a combination capacity of 0.8 must be applied to the denominator of the referenced equations. Refer to a later section this text or to specific manufacturers. 

To pro dde some external protection against the damage that an external lire can do to a pressure relief valve or rupture disk, this author recommends that these devices be insulated after installation in such a manner as not to restrict their action but to provide some measure of reliable performance, even if the vessel is not insulated. 

Rupture disks are used for the same purpose as safety valves and, in addition, serve to relieve internal explosions in many applications. If the pressure rise can be anticipated, then the volume change corresponding to this change can be calculated by simple gas laws, and the capacity of the disk at the relieving pressure is knowm. The system must be examined and the possible causes of overpressure and their respective relief capacities identified before a reliable size can be determined. See Figure 7-14. 

The vessel nozzle diameter (inside) or net free area for relief of vapors through a rupture disk for the usual process applications is calculated in the same manner as for a safety relief valve, except that the nozzle coefficient is 0.62 for vapors and liquids. Most applications in this category are derived from predictable situations where the flow rates, pressures and temperatures can be established with a reasonable degree of certainty. 

Sizing for Combinalion of Rupture Disk and Pressure Relief Valve in Series Combinalion... 

When the rupture disk is installed on the inlet side of the pressure relief valve (see Figures 7-10, 7-11 and 7-12), the ASME code requires that for untested disk-valve combinations that the relieving capacity of the combination be reduced to 80% of the rated relieving capacity of the pressure relief valve [ 1 ]. 

For flow tested combinations, see a few typical data in Table 7-12. Note, for example, that using a Continental disk reverse acting knife blade rupture disc with a Crosby JOS/JBS pressure relief valve that the combined effect is to multiply the rated capacity of the Crosby valve by a multiplier of 0.985 for a set pressure in the 60-74 psig range... 

Using a nomograph requires only the vessel volume in meters, selecting the dust class. St-1, St-2 or St-3 from Table 7-28. Using Tables 7-29 or 7-30 select the Kst value determined experimentally. The reduced pressure, Pfed. (maximum pressure actually developed during a vented deflagration, termed reduced explosion pressure) must not exceed strength of vessel (see earlier discussion) and the Psut, i.e., the vent device release pressure. Note that the static activation pressure, Pjj, must be determined from experimental tests of the manufacture of relief panels such as rupture disks. 

For a flare stack to function properly and to handle the capacity that may be required, the flows under emergency conditions from each of the potential sources must be carefully evaluated. These include, but may not be limited to, pressure relief valves and rupture disks, process blowdown for startup, shutdown, upset conditions, and plant... 

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